Myocardial preconditioning (PC) protects the heart from the consequences of ischemic heart disease and ischemia - reperfusion injury. Catecholamines released during ischemia induce myocardial PC by activating alpha1-adrenoceptors(AR) in the heart. Two alpha1-AR subtypes are expressed in the heart. Recently, in alpha1-AR subtype knockout (KO) mice, each alpha1-AR subtype was found to activate different:signaling pathways. The broad objective of this project is to define the subtype(s) that are responsible for catecholamine induced PC, the mechanisms by which PC is induced, and ultimately whether therapeutics can be utilized to capitalize on subtype specific signaling to benefit cardiac health. The alpha1-AR subtype(s) responsible for catecholamine induced early and late PC will be determined using alpha1-AR subtype KO mice in loss of function studies. An in vivo mouse model of ischemic PC will be used to study the effect of alpha1-AR- and ischemia- induced PC on infarct size. An in vitro mouse Langendorf heart model will be used to study the effect of alpha1-AR- and ischemia- induced PC on myocardial stunning. Subtype specific signaling cascade studies will focus on antiapoptotic signaling via PI3K/AKT, reactive oxygen species, protein kinase C, mitogen activated protein kinases, and tyrosine kinase activation during preconditioning protocols. Signaling complexes formed at each subtype that can account for differences in subtype signaling will be studied using tagged alpha1A and alpha1B subtypes in immunoprecipitation experiments. Late PC requires gene transcription. We have identified several candidate genes that may participate in late PC. The regulation of gene expression and how these gene products contribute to PC will be studied. The ability to precondition the heart for prolonged periods would be an important contribution to many clinical applications where:the heart is exposed to or at risk during prolonged ischemic heart disease or with ischemia - reperfusion injury. The benefits of overexpressing and enhancing alpha1-AR subtype-specific signaling responsible for PC will be tested using a gene therapy approach. The subtype will be expressed in the heart acutely using an adenovirus vector.